docstr: Determine if a server default is a SQL expression or a constant.
  
  There are too many assertions that expect server defaults to round-trip
  identically without parenthesis added so we will add parens only in
  very specific cases.
docstr_tok: ["Determine","if","a","server","default","is","a","SQL","expression","or","a","constant",".","There","are","too","many","assertions","that","expect","server","defaults","to","round-trip","identically","without","parenthesis","added","so","we","will","add","parens","only","in","very","specific","cases","."]
code: def _guess_if_default_is_unparenthesized_sql_expr(
      self, expr: Optional[str]
  ) -> bool:
      """Determine if a server default is a SQL expression or a constant.
  
      There are too many assertions that expect server defaults to round-trip
      identically without parenthesis added so we will add parens only in
      very specific cases.
  
      """
      if not expr:
          return False
      elif re.match(r"^[0-9\.]$", expr):
          return False
      elif re.match(r"^'.+'$", expr):
          return False
      elif re.match(r"^\(.+\)$", expr):
          return False
      else:
          return True
  
imports: from __future__ import annotations
  import re
  from typing import Any
  from typing import Dict
  from typing import Optional
  from typing import TYPE_CHECKING
  from typing import Union
  from sqlalchemy import cast
  from sqlalchemy import JSON
  from sqlalchemy import schema
  from sqlalchemy import sql
  from .base import alter_table
  from .base import format_table_name
  from .base import RenameTable
  from .impl import DefaultImpl
  from ..None import util
  from ..util.sqla_compat import compiles
label_desc: Use image node_id 5 for calling the SQLiteImpl obj's underlying member method code with example usage: obj._guess_if_default_is_unparenthesized_sql_expr(expr) and returns: False, False, False, False, True